Sprockets are commonly used to drive chains in a wide range of industrial applications. As depicted in FIG. 5, a conventional prior art sprocket 13 has a plurality of circumferentially spaced teeth. Sprocket 13 is fixed, via flange 9 and hub 10, on drive shaft 14 which is drivingly rotated as indicated by arrow 16 to rotate sprocket 13. A chain comprising conventionally interlinked barrel portions 5 and link portions 15 is entrained over sprocket 13 and propelled forwardly or backwardly, depending upon the direction of rotation of drive shaft 14.
Some prior art sprockets consist of a single unitary piece which can be welded to a hub. Other prior art sprockets are cast to form the sprocket, flange and hub as a single assembly. Still other prior art "split" sprockets consist of two halves which can be bolted onto a hub flange. Sprockets are typically made of steel, cast iron or plastic.
Significant friction forces are produced as the sprocket propels the chain. These forces wear the sprocket at its points of contact with the chain. Specifically, the driven side of the sprocket groove between each pair of sprocket teeth eventually shows signs of wear due to engagement of the chain barrel portions within the sprocket groove. The sprocket is preferably replaced when such wear becomes apparent.
If a worn sprocket is not replaced reasonably promptly then the worn sprocket regions increase in size. The worn regions initially appear as indentations in the driven side of the sprocket groove. The indentations elongate as wearing progresses, increasing the gap between the teeth at the bottom of the sprocket groove. When the chain direction is reversed, the chain barrel portions must travel an increased lateral distance along the widened gap, producing chain slack which causes the sprocket to hammer against the chain (i.e. backlash). The degree of sprocket (and chain) wear is compounded over time. If neglected, both sprocket and chain can be seriously damaged, resulting in potential equipment breakdown.
Sprocket replacement can be time-consuming, labour-intensive and expensive. For example, if the sprocket is welded onto a hub assembly (as is common), the entire assembly must be removed and replaced. This can be particularly time-consuming and expensive if the sprocket-hub assembly is mounted in a location which is not easily accessible, such as within a conveyor belt drive assembly.
Worn split sprockets are more easily replaced, since they are bolted to the hub flange and do not typically require removal or replacement of the entire sprocket and hub assembly. However, split sprockets are not suitable in many applications, because the bolts which couple the sprocket halves to the hub can be loosened or sheared by sudden jarring, vibration or other substantial forces typically encountered in normal sprocket operation. Moreover, split sprockets do not address the aforementioned wearing problem.
It is sometimes possible to reposition the sprocket in a manner which can reduce wearing somewhat. For example, in some bulldozers, the sprockets are elevated considerably with respect to their conventional positions between the bulldozer tracks. This reduces the degree of articulation of the tracks around the sprockets, which in turn reduces the required area of contact between the tracks and sprockets, thus reducing wear on both parts. However, this technique necessarily lengthens the tracks, and does not eliminate but merely defers somewhat the eventual need for replacement of worn sprockets.
Another commonly employed technique for reducing wear of both chain and sprocket involves installation of the chain itself. Specifically, if the chain is installed with the wide part of each link forward in the direction of chain travel, then chain and sprocket wear is reduced somewhat in comparison to the situation in which the chain is installed with the narrow part of each link forward. However, wear still occurs, and worn sprockets must eventually be replaced.
The present addresses the sprocket wear problem.